Rechargeable lithium batteries use a material from or into which lithium ions are deintercalated or intercalated for positive and negative active materials. For an electrolyte, an organic solvent or polymer is used. Rechargeable lithium batteries produce electric energy as a result of changes in the chemical potentials of the active materials during the intercalation and deintercalation reactions of lithium ions.
For the negative active material in a rechargeable lithium battery, metallic lithium was used in the early days of development. Recently, however, carbon-based materials, such as amorphous carbon and crystalline carbon, are extensively used in place of the metallic lithium due to problems of high reactivity toward electrolyte and dendrite formation of the metallic lithium.
For the positive active material in the rechargeable lithium battery, chalcogenide compounds into or from which lithium ions are intercalated or deintercalated are used. Typical examples thereof include, but are not limited to, metal oxide composites such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (0<x<1), and LiMnO2. Manganese-based materials, such as LiMn2O4 and LiMnO2, are easier to prepare and are less expensive than the other materials and are environmentally friendly, but they disadvantageously have of relatively low capacity. LiNiO2 is inexpensive and has high capacity, but it is difficult to prepare in the desired structure. LiCoO2 is relatively expensive, but widely used as it has good electrical conductivity and high cell voltage.
The positive active material may be prepared by a solid state reaction method. For example, LiOH (or Li2CO3) is mixed with Co3O4 at a corresponding equivalent ratio and the mixture is heat-treated at a temperature between 800° C. and 1000° C. to prepare LiCoO2. During the mixing process, another transition metal may be added in solid phase form in order to enhance the charge and discharge characteristics.
Although many advancements have been made for battery technology, demands still exist for further improvements in cycle-life, high rate capability for charge and discharge, and specific capacity characteristics of the active material.